that's the kind of leadership i intend to provide as president of the united states. >> and, of course -- >> senator clinton, that's a clear swipe at you. >> really? >> back then, it was a very different relationship in the midst of an already bitter rivalry. >> while i was working on those streets, you were a corporate lawyer sitting on the board of walmart. >> you were practicing law and representing your contributor in his slum landlord business in inner city chicago. >> but that relationship quickly changed. >> i endorse him and throw my full support behind him. >> just as hillary clinton showed her support for president obama, obama showed his faith in clinton. >> i have no doubt that hillary clinton is the right person to lead our state department and to work with me in tackling this ambitious foreign policy agenda. >> what was hillary clinton's initial reaction when you told her, look, they're actually considering you as a possibility for secretary of state? >> she didn't believe it. >> reporter: he is one of clinton's closest aides. >> i e-mailed her, i think it was the friday